Learning Exercise

Inferring Map Projection Properties from a Map's Graticule

This exercise is intended to give students practice determining whether a map projection has certain properties.
Course: Introduction to GIS and Mapping
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Map Projections used by the U.S. Geological Survey

A collection of scanned images of 18 map projections from the U.S. Geological Survey map projections poster. see more

Exercise

Background Information: Recall the following properties of the graticule on the globe. (Consult a globe if you aren't comfortable with any of the statements; it is critical that you understand each one for this assignment.)1. All quadrangles along a band of latitude have the same area.2. Quadrangles decrease in area as you move toward either pole.3. All meridians and parallels intersect at right angles (except at the poles.)Prorperties 1 and 2 are useful in determining whether a projection is equal-area (equivalent). Specifically, if the quadrangles along a band of latitude are clearly not the same size, or if the quadrangles clearly do not decrease in area as you move toward the poles, you can say that the projection is definitely not equal-area. If you can't say this, the most definitive thing you can say is that the projection may be equal-area.Similarly, properties 3 and 4 are useful in determining whether a projection might be conformal. Specifically, if any of the intersections are clearly not perpendicular, or if the quadrangles do not get narrower* as you move toward the poles, you can say that the projection is definitely not conformal. If you can't say this, the most you can say is that the projection may be conformal.*Note. When projected into two dimensions, you should consider a quadrangle to be "narrower" than another if it is less wide or if it is taller. As you move toward the poles on a conformal map projection, the quadrangles' heights might remain the same while their widths decrease, or their heights might increase while their widths remain the same.Directions:1. Launch your browser and access the following page: "3G on W3: The Great Globe Gallery on the World Wide Web." (See URL above.)2. Click on any of the 18 named map projections.

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Map projections